Does anyone know if there is supposed to be this kind of play in the piston of a vacuum pump for a 300tdi.
Measurement are taken at the end of the stroke and up to the point where the piston meets the spring tension. This allows for 3 mm of freeplay, im not sure if there is such play when it is installed.
I have a ticking noise, i believe it might be the pump, the surface also looks to be a bit hammered.

Mine has the same kind of play as well . Was like that from new.
As for the ticking not sure but you should be able to get a good look at the lobe/lobe's on the camshaft too see how that looks as there is plenty space.

I’ve just changed mine on my 300tdi. I had a hard brake pedal and braking was a bit dubious. No play on the old pump or new one and braking back to ‘normal’! Was your braking being affected.
I got a new one from Turner’s.